What are modern PPC implementations like?
Hardware-wise: PowerPC is a microprocessor developed mainly by the three developing companies Apple, IBM, and Motorola. It is built with reduced instruction-set computer (RISC) which speeds-up the operation of MIPS (million instructions per second). PowerPC is mainly based on IBM’s earlier Power architecture because it has a similar RISC instruction set for microprocessors.
Intel and AMD CPU's are based on CISC architectures. Typically CISC chips have a large amount of different and complex instructions. The philosophy behind it is that hardware is always faster than software, therefore one should make a powerful instructionset, which provides programmers with assembly instructions to do a lot with short programs. In common CISC chips are relatively slow (compared to RISC chips) per instruction, but use little (less than RISC) instruction
PPC Macs refers to the generation of Macintosh computers created in the mid to late 1990s through to 2006 that used PowerPC RISC based chips made by IBM or Motorola. That last PowerPC based Macintosh, the PowerMac G5 stopped being sold in August 2006. The latest version of Mac OS X a PowerPC chip enabled computer was able to run was Mac OS X 10.5 (Leopard) (so long as the computer supported it).
Intel Macs refers to the newer Macintosh computers (since January 2006) that use Intel's CISC processors. Intel Macs uses EFI instead of BIOS and can run the latest versions of Mac OS X. Intel Macs are also able to run PowerPC compiled applications through a translation layer called Rosetta which is optionally installed in 10.6.
If a program is made available as a Universal binary it is able to run on both PPC and Intel Macs however many new applications released today are Intel only (eg. Google Chrome, Final Cut Studio, Mac OS X Snow Leopard).